The paper presents a case study on the synthesis of labelled transition systems (ltss) for process calculi, choosing as testbed Milner’s Calculus of Communicating System (ccs). The proposal is based on a graphical encoding: each ccs process is mapped into a graph equipped with suitable interfaces, such that the denotation is fully abstract with respect to the usual structural congruence. Graphs with interfaces are amenable to the synthesis mechanism based on borrowed contexts (bcs), proposed by Ehrig and König (which are an instance of relative pushouts, originally introduced by Milner and Leifer). The bc mechanism allows the effective construction of an lts that has graphs with interfaces as both states and labels, and such that the associated bisimilarity is automatically a congruence. Our paper focuses on the analysis of the lts distilled by exploiting the encoding of ccs processes: besides offering some technical contributions towards the simplification of the bc mechanism, the key result of our work is the proof that the bisimilarity on processes obtained via bcs coincides with the standard strong bisimilarity for ccs.

Abstract. Web services are emerging as a promising technology for the development of next generation distributed heterogeneous software systems. We define a new behavioural equivalence for Web services, based on bisimilarity and inspired by recent advances in the theory of reactive systems. The proposed equivalence is compositional and decidable, and it provides a firm ground for enhanced behaviour-aware discovery and for a sound incremental development of services and service compositions. 1

The operational behavior of interactive systems is usually given in terms of transition systems labeled with actions, which, when visible, represent both observations and interactions with the external world. The abstract semantics is given in terms of behavioral equivalences, which depend on the action labels and on the amount of branching structure considered. Behavioural equivalences are often congruences with respect to the operations of the language, and this property expresses the compositionality of the abstract semantics. A simpler approach, inspired by classical formalisms like λ-calculus, Petri nets, term and graph rewriting, and pioneered by the Chemical Abstract Machine [1], defines operational semantics by means of structural axioms and reaction rules. Process calculi representing complex systems, in particular those able to generate and communicate names, are often defined in this way, since structural axioms give a clear idea of the intended structure of the states while reaction rules, which are often non-conditional, give a direct account of the possible steps. Transitions caused by reaction rules, however, are not labeled, since

Symbolic bisimulations were introduced as a mean to define value-passing process calculi using smaller, possibly finite labelled transition systems, equipped with symbolic actions. Similar ideas have been used for modeling with fewer transitions the input behavior of open and asynchronous π-calculus. In this paper we generalize the symbolic technique and apply the resulting theory to these two cases, re-deriving existing results. We also apply our approach to a new setting, i.e. open Petri nets, with the usual result of reducing input transitions. Our theory generalizes Leifer and Milner reactive systems by adding observations.

Reactive systems, proposed by Leifer and Milner, represent a meta-framework aimed at deriving behavioral congruences for those specification formalisms whose operational semantics is provided by rewriting rules. Despite its applicability, reactive systems suffered so far from two main drawbacks. First of all, no technique was found for recovering a set of inference rules, e.g. in the so-called SOS style, for describing the distilled observational semantics. Most importantly, the efforts focussed on strong bisimilarity, tackling neither weak nor barbed semantics. Our paper addresses both issues, instantiating them on a calculus whose semantics is still in a flux: Cardelli and Gordon’s mobile ambients. While the solution to the first issue is tailored over our case study, we provide a general framework for recasting (weak) barbed equivalence in the reactive systems formalism. Moreover, we prove that our proposal captures the behavioural semantics for mobile ambients proposed by Rathke and Sobociński and by Merro and Zappa Nardelli.

Web services represent a promising technology for the development of distributed heterogeneous software systems. In this setting, a major issue is to establish whether two services can be used interchangeably in any context. This paper illustrates — through a concrete scenario from banking systems — how a suitable notion of behavioural equivalence over Petri nets can be effectively employed for checking the correctness of service specifications and the replaceability of (sub)services.

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Web services are emerging as a promising technology for the development of next generation distributed heterogeneous software systems. We define a new behavioural equivalence for Web services, based on bisimilarity and inspired by recent advances in the theory of reactive systems. The equivalence is compositional and decidable, and it provides a firm ground for enhanced behaviouraware discovery and for a sound incremental development of services and service compositions.

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Behavioural equivalences of various calculi for modelling distributed systems differ significantly because the properties which can be observed through interaction depend heavily upon their mode of communication. A typical approach to describing the semantics of communicating processes is to provide a labelled transition system (lts) which captures the interaction potential of the individual processes within a larger system. In many cases, a natural rendering of this lts leads to too fine a semantics as unobservability of certain communications is not accounted for. We propose that a standard approach to augmenting ltss allows morally unobservable communications to actually be modelled as unobservables in the semantics. This approach derives from a rule initially given by Honda and Tokoro to account for unobservability of reception in the asynchronous π-calculus. We examine the implications of adding such rules to lts with respect to the proving behavioural equivalences for various synchronisation mechanisms.